Heretofore, apparatus for measuring three-dimensional movement in a living body have been available in the market. For example, an optical jaw movement measuring apparatus is used to measure relative movement of a lower jaw with respect to an upper jaw, which is constructed integrally with a human head. The optical jaw movement measuring apparatus has a light source device mounted on the head or the upper jaw tooth row of an examinee as a fixed source for measuring the movement of the upper jaw of the examinee, and another light source device mounted on the lower jaw tooth row as a fixed source for measuring the movement of the lower jaw.
However, since the light source devices are mounted respectively on the head or the upper jaw tooth row of the examinee and the lower jaw tooth row, the optical jaw movement measuring apparatus is problematic in that the examinee's freedom is greatly limited in measuring jaw movement. Furthermore, the optical nature of the apparatus makes it impossible to make measurements within a shielded space such as an oral cavity.
Other jaw movement measuring apparatus include magnetic jaw movement measuring apparatus. The magnetic jaw movement measuring apparatus are classified into DC magnetic field measuring apparatus for measuring three-dimensional jaw movement by detecting a DC magnetic field generated by a magnetic generator with a magnetic field sensor, and AC magnetic field measuring apparatus for measuring three-dimensional jaw movement by detecting an AC magnetic field generated by a magnetic generator with a magnetic field sensor. Of these measuring apparatus, the DC magnetic field measuring apparatus may possibly have their measuring accuracy and positional accuracy lowered due to externally applied low-frequency noise such as temporal variation in the geomagnetism, the movement of a magnetic body, etc.
The magnetic field sensor of the AC magnetic field measuring apparatus comprises a triaxial coil. When the magnetic field sensor is inserted into an oral cavity, a magnetic field detected by the magnetic field sensor is transmitted through a cable to a signal processor or the like. Since it is difficult to install the triaxial coil and the cable reliably in the oral cavity, when the examinee makes a jaw movement, the magnetic field sensor tends to fluctuate, thereby increasing the measuring error and reducing the positional accuracy of the magnetic field sensor. It is thus difficult to. reproduce the jaw movement accurately. Furthermore, inasmuch as the components mounted in the oral cavity are large, the examinee's freedom is greatly limited in measuring jaw movement.
In view of the foregoing problems, a magnetic jaw movement measuring apparatus 200 shown in FIG. 17 has been proposed (see Patent Document 1). The magnetic jaw movement measuring apparatus 200 includes a spherical shell 202, six circularly wound field coils 204 disposed in the spherical shell 202, an attachment 210 rigidly coupled to the lower jaw 208 of an examinee 206 in the spherical shell 202, and a sensor coil 212 coupled to the attachment 210 and comprising three choke coils.
Of the six field coils 204, every two field coils 204 make up a uniaxial coil. While alternating currents are flowing through the field coils 204, generating a magnetic field, when the examinee 206 moves the lower jaw 208 with respect to the upper jaw 214, the sensor coil 212 on the attachment 210 is tilted, changing the amplitude of an AC signal that is induced in the sensor coil 212. The amplitude is detected to measure the three-dimensional movement of the lower jaw 208.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2000-193409